Sound recording system



c. N. BA1-'SEL SOUNDv RECORDING SYSTEM Filed July 29. 1959 os ExPos-mes jig. ,2.

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wzffefhf@ @www Patented Jan. 6, 1942 SOUND RECORDING SYSTEM CecilN. Batsel, Los Angeles, Calif., assignor to Radio Corporation of America, a corporation of Delaware Application July 29, 1939, serial No. 287,304 e iy claims. (C1. 417o- 1003 This invention relates to sound film recording systems and particularly to a system for variable density recording wherein the sound track is composed of a plurality of equal length parallel lines of varying opacities.

It is well known that two general types of recording systems are used commercially, one being the variable area type wherein a trace or traces on the lm divide opaque and transparent areas of different widths, and the other being the variable type wherein the sound track is as mentioned above. It is also well known that both of these systems employ noise reduction'. Noise reduction is applied to the area system by making opaque the portions of the sound track area which are not utilized for the traces andis applied to the density system by modulating the light beam about a` point on the density exposure characteristic which varies in accordance with the amplitude of the modulations.

The present invention, therefore, is directed to a sound lm recording system which is readily convertible from variable area to variable density or vice versa, and in both of which noise reduction is applied. Such a system is desirable since. each type of track or sound record has its own advantages from both the recording and reproduction 'standpoints With the present invention the recording apparatus may be quickly' altered with the minimum amount of adjustment to produce either type of record.

An object of the invention, therefore, is to facilitate the recording of sound on motion picture nlm.

Another object of the present invention is to facilitate the transition of a sound recording system from the variable area type to the variable density type and vice versa.

Another object of the invention is to improve the recording of a variable density record with noise reduction.

Although the novel features which are believed to be characteristic of this invention are pointed out with particularity in the appended claims, the manner of its organization and the mode of its operation will be better understood by referring to the following description read in conjunction with the accompanying drawing forming a part thereof in which Fig. 1 is a diagrammatic view of a recording system embodying the invention; and

Fig. 2 is a graph showing an exposure-density characteristic of a film.

Referring no-w toJFig. 1, a light source 5 produces light Which is collected by a lens 6 and 9 operated by a coil I0 as disclosed and claimed in U. S. Patents 2,102,776, 2,102,777 and 2,102,778. The light passing the aperture -8 and shutters 9 is projected on a galvanometer mirror I4 having an actuating coil I5, the light beam then beingreflected by the mirror to a slit mask I1 having a slit I8 thereon. The shape of the light beam impinging `on the mask vI'I at times of no signal is shown by the shaded area I9. The light passing the slit I8 of the mask I1 is projected on the sound track area 2| of a film 22 by a spherical lens 24 and a cylindrical lens 25 to produce the variable density type of track as shown at 2 I The sound wavest'o be recorded are impressed upon a microphone 21 feeding a main amplifier 28, the output of which is divided, a portion going to an amplifier 29 and then to the actuating coil I5 of a galvanometer, and the other portion to a rectifier-amplifier 30 which is connected to the actuating coil I0 of the noise reduction shutters 9.

As disclosed in the above-mentioned patents with the exception of lens 25, this is a standard variable area recording arrangement wherein the M-shaped light beam is vibrated normal to the slit I8, the slit being focused on the film to produce oppositely opposed traces bound by the traces formed b-y the shutters 9. The track produced by this system is the standard duplex variable area track well known in the art. However, With the present invention the cylindrical lens 25 destroys the image of the slit I8 in the horizontal plane so that as the light passes different portions of the slit I8, it only varies the intensity of the line of light on the sound track area 2I and not the length of the beam transversely of the lm so that a variable density track results.

This variable density type of track, of course, would result without the action of the noise reduction shutters 9. However, the noise reduction shutters do introduce noise reduction in the recording since they control the amount of light passing the end portions of the slit I8 in the same manner as they would for variable area recording. For variable area recording, the shutter .edges are imaged on the film, but since this image has been destroyed 4by the cylindrical lens, the noise reduction shutters simply vary the intensity of the beam striking the film.

To further explain the noise reduction action, reference is made to Fig. 2 wherein a negative exposure-density curve is shown. The proper region on the curve for light exposures is, of course, between points a and b. Without the shutters the exposure of the film at times of no signal corresponds to the point c on the curve while all modulations would occur about this point regardless of amplitude. This condition would make the print too transparent at times of no signal and at low signal amplitudes. With the shutters, however, operating in the same manner as for variable area recording, 100% modulation is still about the point c, since the shutters will be at maximum separation. However, for the smaller signal amplitudes, vthe operating point on the curve about which modulation occurs will be moved toward point a, since the shutters reduce the light falling on the nlm as the signal amplitudes decrease. The negative is thus of greater transparency for the lower amplitudes and, consequently, the print will be correspondingly more opaque.

The action of the rectier-amplier 3l] is so arranged that as the signal increases, the bias current through the coil I0 increases, the shutters being normally set at the minimum distance between each other to pass the desired minimum amount of light at times of no signal. Thus, the no signal point is now at point a on the curve instead of at point c; and, as the signals increase in amplitude, the point on the curve about which modulation occurs moves toward point c, the point for full-track modulation.

The system just described, therefore, is readily and quickly convertible for a Variable density system to a variable area system and vice versa by the interchange of the objective lenses between the lm and slit mask, the remaining elements of the system functioning in the same manner without adjustment.

I claim as my invention:

1. A sound recording system comprising a source of light, means for forming the light from said source into a predetermined shaped beam, means for projecting a portion of said beam to a motion picture lm, means for varyng the dimensions of said beam passing said last-mentioned means, and a sphericabcylindrical lens combination for destroying the image of said beam as impressed on said film only in a direction transversely of said nlm for producing a line of light of varying intensity.

2. A sound recording system comprising a source of light, means for forming said light into a predetermined shaped beam, means for varying the shape of said beam in accordance with the average value of the sound waves being recorded, means for passing a portion of said beam to a film, means for varying the length of said beam passing said passing means in accordance with the instantaneous values of said sound Waves, and means adapted to be interposed between said passing means and said film for producing a variable density sound track record by destroying the image of said light beam only in a direction transversely of said nlm.

3. A sound recording system comprising a source of light, means for forming said light into a predetermined shaped beam, means for varying the shape of said beam in accordance with the average value of the sound Waves being recorded, means for passing a portion of said beam to a lm, means for varying the length of said beam passing said passing means in accordance with the instantaneous values of said sound Waves, and interchangeable means adapted to be interposed between said passing means and said iilm for producing either a variable area or a variable density sound track record, one of said lastmentioned interchangeable means including a spherical-cylindrical lens combination which destroys the image of said light beam transversely of said lm.

4. A sound recording system comprising a light source, a mask for forming light from said source into a beam, shutters for varying the length of said beam in accordance with the average value of sound waves being recorded, a mask having a slit therein, a reflector for reflecting said beam to said slit in accordance with the instantaneous values of said sound waves, and optical means intermediate said slit mask and a film for varying the intensity of the light beam impressed on said film in accordance with the length of said beam passing said slit, said optical means comprising a spherical-cylindrical lens combination.

' CECIL N. BATSEL. 

